Stub the Array::ShapedXArray roles

These roles need stubbing for some reason, otherwise they will cause
"Object does not exist in serialization context" error when trying to
create something inside the Array class, like the Array::Agnostic role
does, which happened after ee08923 and 532b542.

src/core.c/Array.pm6

@@ -5,6 +5,15 @@ my class X::Subscript::Negative { ... };
 my class X::NotEnoughDimensions { ... };
 my class X::Assignment::ArrayShapeMismatch { ... };
 
+# These roles need stubbing for some reason, otherwise they will cause
+# "Object does not exist in serialization context" error when trying to
+# create something inside the Array class, like the Array::Agnostic role
+# does, which happened after ee089234fc and 532b5423f0.
+our role Array::ShapedArray  { ... }
+our role Array::Shaped1Array { ... }
+our role Array::Shaped2Array { ... }
+our role Array::Shaped3Array { ... }
+
 # stub what we need now
 my class array is repr('VMArray') { ... };